1. Field of the Invention
The present invention relates to an X-ray image sensory system, and more particularly, to an X-ray image sensory system with the utilization of the field emission mechanism to move the field emission electrons towards the charge collection layer to determine the input amount of the X-ray.
2. Description of the Prior Art
Conventional technology uses films to display X-ray images. An unexposed film is placed behind the screen, which was able to convert X-ray to the wavelength close to visible light. After the film is exposed, it is processed and printed. Thus the image of the X-ray is shown. In the process of exposure, transportation, processing and printing, it is prone to damages. If that happens, the whole process has to be repeated again from the beginning. As for the storage of the films, the space and the security are two the major concerns of the conventional technology.
The digitalization of the X-ray images, and storing them on the digital media can solve the aforementioned problems like the storage space and the security. Digitalized data is easier for transportation and remote access, which becomes imperative in long distance medical diagnosis. With appropriate image processing, digital images could also be used for disease detection. Therefore, the digitalized X-ray images are superior to the conventional film technology.
Currently, to obtain digitalized X-ray images, a converting material is used to convert the X-ray to signals of light or electricity. Coupled with a photodiode or electron collection device, the X-ray could be converted to electrical signals. Passing through A/D (analog/digital converter), the X-ray images are obtained. This method is called direct, in contrast to that converting X-ray to the visible lights, and the latter is named as the indirect one.
Please refer to FIG. 1 of a schematic diagram of a direct X-ray image sensory system 10. The direct X-ray image sensory system 10 includes a bias electrode 12, a conversion layer 13, a pixel electrode 14, and a TFT capacitor module 16. The bias electrode 12 is to connect with an applied bias voltage. The conversion layer 13, which is a semiconductor material, e.g., Se, with the characteristic of generating electron and hole pairs, is used to convert the X-ray into electron and hole pairs.
It works as follows. The conversion layer converts the X-ray signal to e-h (electron-hole) pairs. Due to the applied bias voltage, the e-h pairs are separated, whereas the electrons are pulled to the pixel electrode 14, which induces equivalent electrons at the electrode. The accumulated electrons are stored in the TFT capacitor module 16. The gate of the TFT capacitor module 16 determines when the electrons are released from the TFT capacitor module 16, which means the emission of the signal. And external sequencer (not shown) is used to control the sequence of the emission. Finally, the A/D converter outputs the digitalized image signal. The conversion layer 13 is usually with the value of several hundred micrometers in thickness. The applied bias voltage for generating the bias electrical field is between 1 KV to 10 KVs. Se is the most commonly used material. In general, only some semiconductor materials, which are able to generate e-h pair, are used in the present invention.
However, since this type of X-ray image sensory system requires a comparatively high voltage (several KVs) due to the fact that the free electrons in Se are with comparatively short life times and low mobility. It makes the manufacturing of such sensory system more difficult, as well as higher protection requirements when in use.
There is another type of indirect X-ray image sensory system, in which no high voltage is employed. Instead, it uses a scintillator to absorb the X-ray, converts the X-ray to visible lights, and uses photodiode to detect visible lights. However, for a large size photodiode, about 4*4 inches to 17*17 inches, the yield for this image sensory panel is very low, leading to much more manufacturing costs.
It is therefore a primary objective of the present invention that the present invention X-ray image sensory system can be operated at a low applied voltage and is with a field emitting architecture for emitting free electrons and collecting corresponding charges to determine the amount of the X-ray.
In accordance with the claimed invention, the present invention includes an electrode layer, a conversion layer, a gap layer, and a charge collection layer. The sensory system employs the xe2x80x9cX-rayxe2x86x92chargexe2x80x9d conversion layer to operate the xe2x80x9cX-rayxe2x86x92charge to field emission electronxe2x80x9d mechanism in an appropriate electric field. The field emission electrons are moved towards the charge collection layer made of semiconductor material. Based on the amount of the charges accumulated within the charge collection layer, the original amount of X-ray exposure can be calculated.
It is an advantage of the present invention that a rough surface of the aforementioned conversion layer is shaped into many coarse tips with small curvature radius to make the electron emission be more convenient. And, the present invention X-ray image sensory system is operated at a low voltage to protect the charge collection layer from damages.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.